Building management systems encompass a wide variety of systems that aid in the monitoring and control of various aspects of building operation. Building management systems (which may also be referred to herein as “building control systems”) include security systems, fire safety systems, lighting systems, and heating, ventilation, and air conditioning (“HVAC”) systems. HVAC systems are sometimes referred to as “environment control systems” because these systems control the environmental conditions within the building. A single building may include multiple building management subsystems (e.g., a security system, a fire system and an environmental control system). Multiple building management systems may be arranged separately from one another or as a single system with multiple subsystems that are controlled by a common control station or server. The common control station or server may be contained within the building or remote from the building, depending upon the implementation.
Intelligent building control provides for control of the building that is user intelligent. That is, based on behavior or predicted behavior of users within the building, the intelligent building control provides the users with intelligent environmental controls, safety controls, logistical, and/or information control. Such user behavior may include the location of people within particular areas of a building, which may be utilized by the building management system to enhance control of the environmental conditions of the building. For example, the system may position motion sensors throughout a building to track occupant activity and deliver timing data corresponding to the detected motion to a central server. The central server will need precise timing data in order to track people accurately.
Some sensors of building management systems do not provide precise timing data. Each motion sensor may include an on-board clock but the clock of one motion sensor may be misaligned in time relative to another motion sensor of the system. Existing systems may address the misalignment in time of motion sensors, but they do so at the expense of added cost and/or insufficient precision. For example, the time of an on-board clock for a particular sensor may be set periodically through a broadcast message provided to the sensor or an external tool but additional components and complexity are added to the system. For another example, the central server may store the time when timing data is received as well as the sensor time, but errors in transmit timing may still exist. Thus, motion sensors of existing systems rely on timing data that lack precision and synchronization with the timing data of other sensors of the system.